The invention relates generally to multichannel heat exchangers employing flow distribution manifolds.
Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Multichannel heat exchangers generally include multichannel tubes for flowing refrigerant through the heat exchanger between manifolds that are connected to a refrigerant inlet and a refrigerant outlet. Each multichannel tube may contain several individual flow paths. As a fluid, such as refrigerant, flows through the flow paths, the fluid may exchange heat with an external fluid, such as air, flowing between the multichannel tubes. Multichannel tubes may be used in heat exchangers of small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems, as well as in vehicle air conditioners, and refrigeration devices of various types.
In general, heat exchangers transfer heat by circulating a refrigerant through a cycle of evaporation and condensation. In many systems, the refrigerant changes phases while flowing through heat exchangers in which evaporation and condensation occur. For example, the refrigerant may enter an evaporator heat exchanger as a liquid and exit as a vapor. In another example, the refrigerant may enter a condenser heat exchanger as a vapor and exit as a liquid. Generally, a portion of the heat transfer is achieved from the phase change that occurs within the heat exchangers. That is, while some energy is transferred to and from the refrigerant by changes in the temperature of the fluid (i.e., sensible heat), more energy is exchanged by phase changes (i.e., latent heat). For example, in the case of an evaporator, the external air is cooled when the liquid refrigerant flowing through the heat exchanger absorbs heat from the air causing the liquid refrigerant to change to a vapor.
In a refrigeration system, an expansion device is located in a closed loop prior to the evaporator. The expansion device lowers the temperature and pressure of the refrigerant by increasing its volume. However, during the expansion process, some of the liquid refrigerant may be expanded to form vapor. Therefore, a mixture of liquid and vapor refrigerant typically enters the evaporator. Because the vapor refrigerant has a lower density than the liquid refrigerant, the vapor refrigerant tends to separate from the liquid refrigerant resulting in some multichannel flow paths receiving mostly vapor. Further, in heat exchangers containing vertical manifolds, gravity may promote separation of the liquid and vapor refrigerant. The tubes containing primarily vapor are not able to absorb much heat, which may result in less efficient heat transfer.